All very well to have a car which produces very little CO2, but what about the energy used to make and scrap a car? I have a 16-year-old VW which does 30-40 mpg; presumably if I behaved as manufacturers would like, I would have bought - and junked - at least three cars in that time. Is this eco-friendly?Graham Cumming, Geneva, Switzerland

This is a good idea in principle. But how efficient and environmentally friendly are these electric cars really? Where does the electricity come from? How efficient are they over the whole process? Are they environmentally level A cars or city pollution friendly level A cars. There is a big difference.Neil Farmer, Glasgow

This is yet another worthless study. Electric vehicles require the electricity to be generated in the first place, in the UK that is mostly from burning natural gas which produces C02. Furthermore no account is taken of the problem of battery disposal, affecting hybrids and electric cars. It also ignores the energy consumed and the pollution that occurs in the production and disposal of the vehicles. On their own, these figures are technically quite worthless and are likely to mislead the public. If one wants a 'green' vehicle then the whole product lifecycle needs to be analysed, from raw material extraction right through to final waste disposal.Richard Ward, UK & USA

The rating of battery electric cars as band A, based on their carbon dioxide (CO2) emissions, is flawed. Zero emission at point of use does not take into account the environmental effects of electricity generation and losses in transmission to charge the batteries. Fossil fuel power stations all emit CO2. David, Sussex

If carbon dioxide is the measure for greenness then anything that burns hydro-carbons is never going to be green. Hydrogen cars produce water vapour (although some NO2 is produced in the combustion process) so could be reasonably green as an internal combustion engine. The real answer would be to discover some new method of power generation - budding Einsteins start here.Rod Main, Newhaven UK

I think it is arguable whether even an electric car can be classed as green since the electricity they run on will still produce emissions whilst its being generated. I think the only personal transport that is really A grade green is the bicycle. I don't think there's anything wrong with demonising 4x4's - they are wasteful, selfish, dangerous and dirty, and its time their owners faced up to the damage they do to our environment.Pete Taylor, London, UK

Rating vehicles only based on Co2 emissions is a flawed generalisation - there are many other combustion by-products produced that are also damaging to the environment. It is also relative - for example if you travel extensively by air, by reducing the number of journeys you make you can have a far larger impact on the environment than by switching to a slightly smaller, more efficient car.Jon Webb, Henley upon Thames